After aspirin treatment, which laboratory finding would you most likely observe?

• A. Prothrombin time prolonged
• B. Partial thromboplastin time prolonged
• C. Bleeding time prolonged
• D. Platelet count decreased

Answer: (C)

Aspirin impairs platelet function by irreversibly inhibiting cyclooxygenase-1, which blocks thromboxane A2 synthesis needed for platelet aggregation. Because this affects how platelets work rather than how the coagulation cascade operates, the initial step of hemostasis is disrupted while the plasma clotting factors remain untouched. Bleeding time measures the duration of bleeding from a standardized skin puncture and reflects platelet function; when platelets can’t aggregate properly, bleeding takes longer to stop, so bleeding time is prolonged. In contrast, prothrombin time and partial thromboplastin time assess the coagulation cascades in plasma and are not significantly altered by aspirin. Platelet count is unaffected by aspirin, since it doesn’t decrease the number of platelets—only their ability to clump together is reduced. Therefore, the most likely lab finding after aspirin treatment is a prolonged bleeding time.